In many electronic systems, and particularly in data processing systems, there is always the need to provide regulated d-c voltages to the logic and other circuitry of the system. Typically, a switching regulated power supply is employed which receives raw d-c (which may have been rectified from a-c mains and filtered), chops this raw d-c (as by alternatively enabling SCRs) at a rate much higher than the alternating rate of the mains (and typically ultrasonic), passes the chopped d-c through a step-down transformer (which, because of the switching frequency of the chopped d-c, need not be massive), rectifies the output from the step-down transformer and regulates and filters the rectified output to obtain a regulated output.
The regulation of switching power supplies is often achieved by feeding back the sensed output voltage to a control circuit in the switching apparatus itself. In switching regulated power supplies of this type, subtle (and even conspicuous) instabilities may occur in the form of oscillations resulting from the effects of feedback obtained from an output filter employing reactive (and thus phase shifting) components in conjunction with the operation of the regulator circuit. This condition (which can cause serious problems in the powered circuitry ranging from insidious intermittent errors to destruction) has been recognized and addressed in the prior art. See, for example, U.S. Pat. No. 4,298,924 (issued November 3, 1981) to Luther L. Genuit, entitled SWITCHING REGULATOR WITH PHASE SHIFT SUBTRACTION, which describes a switching regulator incorporating the concept of employing a feeback voltage obtained by subtracting the phase shift voltage appearing across an output filter choke from the output voltage.
A more general approach has been to use attenuation-phase methods of rolling off the open loop gain of the regulator power amplifier to zero decibels with a phase margin of about 45.degree.. (This technique has sometimes incorporated a first derivative component into the feedback voltage). Still, and as well known to those skilled in the art, even in the prior art switching regulators in which the problem of instability has been addressed, instability may still occur from more subtle sources than the phase shift caused by an output filter choke (or sometimes still from that source even if it has addressed). It is thus to the end of securing more stable operation of switching regulated power supplies, independent of the reasons for tendencies toward instability, that this invention is directed.